Sarah P. Marcum

Previously, Uranus and Neptune were considered ice giants because of assumed thick layers of frozen water, methane, and ammonia. New calculations paint a different picture: deep inside them hides an ocean of hot magma, which under immense pressure has absorbed a colossal amount of hydrogen.

In the depths of sub-Neptunes, the most common type of planet in the Galaxy, though not one you could stand on, silicate magma and hydrogen mix into a single supercritical cocktail. Previously, it was thought that beneath the dense hydrogen atmosphere lay a sharp boundary with molten silicate, like oil on water.